Process for preparing crystalline mixed metal oxides

Abstract

An improved process for preparing crystalline mixed metal oxides, such as barium titanate, in which an organometallic compound is reacted simultaneously and continuously with a solution of a divalent alkaline earth metal ion in an alkaline high turbulence energy environment, the reaction product is crystallized, and the crystals are isolated.

What is claimed is: 
     
       1. A process for preparing crystalline mixed metal oxides having simultaneously a narrow particle size distribution and low surface area of the formula:   ABO.sub.3     wherein,   A is metal cation selected from Ba, Sr, Ca, Mg, Pb and Nd and mixtures thereof; and B is metal cation selected from Ti, Zr, Nb, Hf, Zn and Sn and mixtures thereof which comprises the steps of:   (a) simultaneously and continuously mixing an organometallic compound, mixture of organometallic compounds or a hydrolyzable system, of the structure BL n , where B is as defined above, L is a hydrolyzable group, or a combination of such groups, selected from alkoxy, aryloxy, aminoalkoxy, acetoxy, acetoacetonyl, chlorides, nitrates, and acetates, and n is 2 or 4 with a solution of a compound, or a mixture of compounds, of the general structure AX y , where A is as defined above, X is an anion, or combination of anions, selected from hydroxide, chloride, nitrate and acetate, and y is 2 or 3 in an alkaline, high turbulence energy environment characterized by a turbulence intensity greater than 9×10 6  cm/sec 3  ;   (b) crystallizing the reaction product; and   (c) recovering crystals wherein 90% of particles are greater than 0.2 μm in size up to about 1.0 μm in size, the surface area is less than 15 m 2  /g and the A/B mole ratio is from 0.990 to 1.020.   
     
     
       2. The process of claim 1 wherein the solution of A cations is an aqueous solution. 
     
     
       3. The process of claim 1 wherein the solution of A cations is a non-aqueous solution. 
     
     
       4. The process of claim 1, 2, or 3 in which the organometallic compounds BLn are premixed with a nonionic surfactant to form a first ingredient stream which is reacted with the solution of compounds AX y  as a second ingredient stream by mixing said streams simultaneously and continuously in a high turbulence energy environment. 
     
     
       5. The process of claim 4 wherein said mixing comprises pumping said ingredient streams simultaneously through a coaxial jet mixer. 
     
     
       6. The process of claim 4 wherein said organometallic compound BL n  is tetrabutyl titanate and said surfactant is an ethoxylated alkylphenol. 
     
     
       7. A process for preparing crystalline barium titanate having 90% of the particles greater than 0.2 μm in size up to about 1.0 μm in size, and a surface area of less than about 15 m 2  /g which comprises the steps of: (a) reacting tetrabutyl titanate as a first ingredient stream with a solution of barium hydroxide as a second ingredient stream at a temperature of 80°-85° C. in a high turbulence energy environment comprising pumping said ingredient streams simultaneously through a coaxial jet mixer, said environment characterized by a turbulence intensity greater than 9×10 6  cm/sec 3  to form a slurry and discharging said slurry into an alkaline heel of water;   (b) crystallizing said slurry by heating under reflux with continuous agitation for at least about 6 hours to no more than 48 hours; and   (c) recovering said crystals.   
     
     
       8. A chemically homogeneous crystalline mixed metal oxides having a narrow particle size distribution and low surface area of the formula:   ABO.sub.3     wherein,   A is metal cation selected from Ba, Sr, Ca, Mg, Pb and Nd and mixtures thereof; and   B is metal cation selected from Ti, Zr, Nb, Hf, Zn and Sn and mixtures thereof which are prepared by a process comprising the steps of:   (a) simultaneously and continuously reacting an organometallic compound, or mixture of organometallic compounds, of the general structure BL n  where B is as defined above, L is a hydrolyzable group, or combination of such groups, selected from alkoxy, aryloxy, aminoalkoxy, acetoxy, and acetoacetonyl, and n is 2, 4, or 5 as a first ingredient stream with a solution of a compound, or a mixture of compounds, of the general structure AX y , where A is as defined above, X is an anion, or a combination of anions, selected from hydroxide, chloride, nitrate and acetate, and y is 2 or 3 in an alkaline, high turbulence energy environment comprising pumping said ingredient streams simultaneously and continuously through a coaxial jet mixer characterized by a turbulence intensity greater than 9×10 6  cm/sec 3  ;   (b) crystallizing the reaction product for at least 6 hours to no more than 48 hours; and   (c) recovering crystals wherein 90% of particles are greater than 0.2 μm in size up to about 1.0 μm in size, a surface area of less than about 15 m 2  /g and an A/B mole ratio in the range of about 0.990 to about 1.020.   
     
     
       9. The crystalline mixed metal oxide of claim 8 which is barium titanate or strontium titanate. 
     
     
       10. The crystalline mixed metal oxide of claim 9 which is doped with one or more ions selected from Nd, Nb, Zn and Zr. 
     
     
       11. The process of claim 1 wherein the crystalline mixed metal is a solid solution of barium titanate, barium zirconate and barium zinc niobate; the hydrolyzable system is a mixture comprising anhydrous zinc chloride, niobium (V) Chloride, zirconium-propoxide and tetrabutyl titanate, and the alkaline earth metal hydroxide is barium hydroxide. 
     
     
       12. The crystalline mixed metal oxide of claim 8 is a solid solution of barium titanate, barium zirconate and barium zinc niobate.